1. Field of the Invention
The present invention relates to data transfer using parallel optical transmission, in particular, to a parallel optical reception module for receiving optical data signals through a plurality of parallel data channels, and/or a parallel optical transmission module for transmitting optical data signals through a plurality of parallel data channels.
2. Description of the Prior Art
In the field of computer systems, the improvement in calculation or processing capability is supposed to require faster and larger data transfer between computers. Faster data transfer has been realized by the establishment of data transfer using optical transmission. However, larger data transfer apparently has not yet been realized sufficiently.
The implementation of larger data transfer is supposed to require xe2x80x9cparallelxe2x80x9d optical transmission in data transfer. However, the parallel optical transmission has suffered from a problem such that skews or time lags could be generated between parallel data channels because of the difference in data transmission rate of optical fibers and in processing rate of photodetectors for converting optical signals to electric signals. The skew would make computers incapable of calculating or processing received data signals. The further the transferred data should reach, the larger the skew gets. Skews are obstacle to implementation of parallel optical transmission in data transfer.
It is accordingly an object of the present invention to provide a parallel optical transmission/reception module realizing a larger and longer data transfer using parallel optical transmission by detecting and/or correcting skews between parallel data channels.
According to a first aspect of the present invention, there is provided a parallel optical transmission module comprising a skew data transmission unit capable of transmitting parallel synchronous pattern signals for a plurality of parallel data channels.
According to a second aspect of the present invention there is provided a parallel optical reception module comprising a skew data reception unit capable of taking out parallel pattern signals synchronously transmitted from other side in a plurality of parallel data channels and detecting a skew between the data channels based on the parallel pattern signals.
With a combination of the above parallel optical transmission and reception modules, it is possible to easily detect a skew between the parallel data channels by transferring the parallel pattern signals in the respective parallel data channels. In this case, the parallel pattern signals preferably have wavelength different from that of parallel data signals transferred in the parallel data channels. Difference in wavelength between the pattern signal and data signal enables employment of a single optical fiber common to the transfer of the pattern signal and data signal.
The parallel pattern signals may be transferred with or without the transfer of the data signals. Accordingly, a skew can be detected prior to the transfer of the data signals, and even during the transfer of the data signals. When the parallel pattern signals are transferred along with the data signals, the pattern signals are multiplexed on the data signals. The parallel pattern signals having wavelength different from that of the data signals enables easy extraction of the parallel pattern signals from the multiplexed signals. If the transfer the parallel pattern signals is kept with or without the transfer of the data signals, a skew can be detected immediately after the skew has varied.
The parallel optical reception module may further comprise a skew correction circuit capable of correcting the skew of the data signal based on the skew detected by the skew data reception unit. The skew correction circuit serves to output the parallel data signals without skews. Accordingly, the parallel data may simultaneously be subjected to processing or calculation.
On the other hand, a parallel optical transmission module may comprise a skew data reception unit capable of taking out parallel pattern signals synchronously transmitted from other side in a plurality of parallel data channels and detecting a skew between the data channels based on the parallel pattern signals. In addition, the parallel optical transmission module may further comprise a data transmission circuit capable of transmitting parallel data signals with the skew corrected based on the skew detected by the skew data reception unit into the parallel data channels. If the parallel data signals are transmitted with time lags corresponding to the length of the detected skews, a parallel optical reception module can simultaneously receive the parallel data signals under the effect of the skews.
When the skew data reception unit is assembled in a parallel optical transmission module, the parallel data signals may be transmitted after the reception of the parallel pattern signals are confirmed. The transfer after the confirmation serves to inspect the connection between the parallel optical transmission and reception modules by optical transmission paths such as optical fibers. In this case, it is possible to apply Class 1 regulation in the laser safety regulation to the transmission of optical pattern signals while applying Class 4 regulation to the transmission of optical data signals, so that larger power may be obtained according to Class 4 regulation for data transmission, and at the same time, reduced requirements can be applied to handling of the modules according to Class 1 regulation. It is possible to realize an open fiber control system.
Further, according to a third aspect of the present invention, there is provided a determination circuit for a later data channel, capable of outputting a pattern signal in a first data channel at a point when a phase difference is generated between the pattern signal in the first data channel and a pattern signal in a second data channel, said channels having a skew. The determination circuit serves to detect the level of a signal in the first data channel at a point when the skew between the first and second data channel causes the phase difference. Accordingly, the later data channel which receives data later than the other data channel can be identified by the level (high or low) of a signal in the first data channel.
The determination circuit may be implemented by: an exclusive OR gate capable of detecting a difference in level between a pair of pattern signals, said difference being caused by a phase difference in first and second data channels having a skew; and a flip-flop circuit capable of receiving an output of the exclusive OR gate at a clock terminal and a pattern signal in the first data channel at a data terminal. This type of the determination circuit allows the exclusive OR gate to output a high level pulse signal corresponding to the skew generated between the first and second data channels. The duration or length of the pulse signal serve to represent the phase difference between the pattern signals, namely, the length of the skew. The flip-flop circuit serves to store the later data channel. Here, parallel synchronous pattern signals are preferably transferred in the first and second data channels.
The determination circuit may further comprise a further flip-flop circuit between the output of the exclusive OR gate and the clock terminal for switching over high level and low level signals at the clock terminal in response to rise in the output of the exclusive OR gate. The further flip-flop circuit serves to identify a later data channel even when the later data channel shifts from one data channel to the other.
The pattern signal in the first data channel may be supplied via a delay circuit to the data terminal in the aforementioned determination circuit. The delay circuit serves to reliably identify a later data channel irrespective of the transmission delay inevitably generated in the exclusive OR gate and the flip-flop circuit.